A common mode of electronic packaging involves affixing semiconductor devices onto substrates by means of an adhesive or encapsulant. The more prominent uses are the bonding of integrated circuit chips to lead frames or other substrates, and the bonding of circuit packages or assemblies to printed wire boards. Some of the performance properties for these applications are provided by the use of thermosetting materials for the adhesives or encapsulants.
U.S. Pat. No. 6,265,530 discloses an adhesive composition for use in electronic devices that comprises thermosetting polyfunctional maleimide compounds, polyfunctional vinyl compounds, and suitable curing initiators.
It is known that a monofunctional 2-oxazoline will react with a mono-functional vinyl compound such as p-chlorophenylmaleimide through a zwitterion polymerization (Rivas, B. L.; Sanhueza, E. Polymer Bulletin 1999, 42, 281, and references cited therein). Solution spontaneous copolymerization of 2-methyl-2-oxazoline as the nucleophilic monomer with p-chlorophenylmaleimide as the electrophilic monomer in the absence of initiator provided linear polymeric materials. However, these materials are not thermosetting materials.
The inventors discovered that the use of a bisfunctional oxazoline as a nucleophilic monomer in zwitterion polymerization in bulk provides materials capable of being thermoset.